Field of the Invention
The invention relates to processes for manufacturing ophthalmic lenses, including a laser-marking step for producing permanent engravings on a surface of the ophthalmic lens.
The invention also relates to a computer program including instructions configured to implement each of the steps of such a manufacturing process, to a command/control unit including system elements configured to execute a computer program implementing each step of such a manufacturing process and to a laser-marking machine including such a command/control unit.
The invention also relates to a client-server communication interface for transferring a computer program implementing each step of such a manufacturing process to a remote computer and its execution on this computer, or for transferring input and output data.
Description of the Related Field
It is known that ophthalmic lenses undergo various manufacturing steps. The manufacturing processes generally employed to obtain a finished lens edged to the shape of a particular frame typically comprise steps in which the surface of the ophthalmic lens is provided with markings which are referred to as permanent markings.
These markings may be formed by engravings, or micro-engravings, representing points or crosses and identifying a particular point (for example the optical center of the ophthalmic lens or the prism reference point for a progressive lens), or axis lines (for example for indicating the horizontal axis along which astigmatism is corrected), or shapes delimiting a particular zone (for example a near vision zone or a far vision zone in the case of a progressive ophthalmic lens).
Likewise, it may be necessary to produce markings allowing the lens to be identified, or other commercial markings.
These permanent markings are quite often produced on a concave face of the ophthalmic lens, this face being referred to as the back face.
In a process for manufacturing an ophthalmic lens, the latter is blocked, for example via its convex face, referred to as the front face, so that the concave surface of its back face can be machined by turning. Next, this machined concave surface is polished before undergoing one or more marking operations. Following these operations, which are more generally referred to as surfacing (machining and polishing) and marking operations, the ophthalmic lens is unblocked and cleaned before undergoing steps in which it is colored and/or varnished (in other words various layers of various functional compositions, such as an antireflection coating, an antifog coating, an anti-scratch coating, an anti-smudge coating, etc., are applied) and/or the lens is printed (in other words printed markings are produced using ink, these markings being what are referred to as temporary markings). The available and applied coatings are increasingly numerous and diverse and hence manufacturing processes are increasingly complex and place more and more stresses on the ophthalmic lens.
Permanent markings are generally produced using laser-marking machines emitting light radiation of wavelength comprised between about 3 μm and about 50 μm, in other words in the mid- to far-infrared. The effect of these laser-marking machines on the ophthalmic lens is that of a thermal marker that produces deformations in the material on the back face of this ophthalmic lens.
These deformations are characterized by geometric characteristics, such as a diameter and/or a depth, that are representative of an operating point of the laser-marking machine.
These deformations are in fact small recesses, also referred to as craters, formed in the surface of the ophthalmic lens. These recesses are surmounted by rims on this surface, which take the form of small peaks of material.
The deformations are sensitive to thermal stresses that the ophthalmic lens may be subjected to subsequent to the production of these markings. Now, the aforementioned coloring and/or varnishing steps may be carried out at temperatures of about 60° C. to 90° C., or even higher. For example, the varnishing step may comprise heating to a temperature of about 75° C. to about 85° C., in order to fix the varnish to the surface of the ophthalmic lens.
These temperatures inflict high thermal stresses on the ophthalmic lens because they are similar to stress relaxation threshold values of the lens (one may also express that as creep stresses). Thus, when the lens undergoes these steps, the recesses produced during the marking may be at least partially filled in (by contraction of the rims, or even contraction of the internal walls of the recesses). Thus, when the ophthalmic lens has undergone these steps and it is finished or almost finished, the markings referred to as permanent may be less visible, or even have at least partially disappeared.
The operating point of the laser-marking machine is not without effect on the conformity of the markings produced on the surface.
Thus, recesses of very large diameter may allow the effect of the high thermal stresses that an ophthalmic lens may be subjected to to be mitigated; however, this will affect the visibility thereof, such markings being too readily visible on the finished lens and possibly annoying the wearer of this lens, in addition to being unaesthetic. In contrast, recesses of too small a diameter, although they should not cause the wearer any annoyance, may affect conformity as these recesses could no longer be visible at all.
Generally, for any given manufacturing process, and in particular for given steps subsequent to the marking steps, trials are to be carried out in order to determine an optimal operating point of the laser-marking machine, but this decreases productivity.